The present invention relates to a sensor probe for measuring hydrogen concentration in molten metal and method for measuring hydrogen concentration in molten metal using said sensor probe.
Conventional methods for measuring hydrogen concentration in molten metal are (1) the initial bubble method calculating the amount of hydrogen gas based on the pressure and temperature of sample at the time the first bubble is formed on the surface of sample under reduced pressure, (2) the reduced pressure solidification method which measures the amount of hydrogen gas based on the observation of the formation of bubbles in the sample which solidifies under reduced pressure, comparing the specific gravity with that of the standard and the bubble formation on the cross section of the sample, and (3) the Telegas method which injects a small amount of gas into molten metal, collecting the discharged gas after circulation in said molten metal and analyzing the hydrogen gas in said discharged gas using gas chromatography after the distribution of hydrogen gas in said discharged gas reaches its equilibrium state.
These methods, however, have several disadvantages such as too much time is consumed which precludes practically use at the casting site, lower accuracy, larger size of equipment and too much cost for determination.
The present inventors have provided a method for measuring hydrogen concentration in molten metal which employs a galvanic cell type hydrogen sensor using SrCe.sub.0.95 Yb.sub.0.05 O.sub.3-x as a solid electrolyte, which shows proton conductivity at high temperature. The method is based on the electromotive force generated by the difference of hydrogen activity between the partial pressure of hydrogen on the reference electrode of said sensor and the hydrogen concentration in molten metal measured using said hydrogen sensor. According to this method, there are several advantages such that cost for measuring hydrogen concentration is lower, the measuring process can be completed within a shorter time, changes of hydrogen concentration in molten metal can be measured continuously as electromotive force, and the like.
However, this method has a disadvantage that continuous operation for longer time is difficult because solid electrolyte is reduced by the molten metal and oxide layer is formed on the interface between the solid electrolyte and the molten metal in case of molten metal having a very low partial pressure of oxygen in equilibrium in molten metal, particularly aluminum. That is, when a sensor probe was dipped directly in molten metal for measuring hydrogen concentration in molten metal using proton conductive solid electrolyte, an insulating oxide layer forms on the interface between molten metal and solid electrolyte in a range of temperature from 400.degree. to 1100.degree. C. This layer disturbs measurement of hydrogen concentration.